General description
UM0527
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1.2.11 Inverter
The inverter is controlled by signals generated by the PWM module. In battery working
mode the microcontroller generates two signals: INV_A and INV_B. The frequency depends
on the firmware version: EU - 50 Hz, US - 60 Hz. The duty cycle is less than 50% and
depends on the voltage of the DC/DC converter. The phase of the INV_B signal has to be
shifted by a half time period to INV_A. The inverter is controlled by a timer interrupt. The
frequency of the interrupt is 32 times higher than the mains frequency: every half-period is
divided into 16 steps, and the number of steps is stored in a global variable.
Before any steps the SHD signals are checked and if they are inactive (H), the inverter
signals are switched off (rise to H).
Buffered working mode
< 26,8
L
>= 27,8
H
Table 15.
Battery charge modes (continued)
Step of charge
process
Battery
voltage
CHOFF
Description
Table 16.
SHD signals
Step
no
SHD
Description
1
Fall to L
Proper inverter signal falls to L.
2 - 13
L
In any steps the squared value of the output voltage accumulates. The
accumulated value is compared with the nominal RMS output constant, and if it is
greater, the SHD signal rises to H.
14 - 15
H
16
H
The accumulated value of the output voltage is cleared, the variable storing a step
is not cleared. The inverter phase is changed to the opposite state.
